It is known in the art of internal combustion engines to provide variable valve actuation devices which are switchable between a low lift mode and high lift mode, thereby opening a combustion valve, for example an intake valve, to a low lift and a high lift respectively. One such variable valve actuation device is disclosed in United States Patent Application Publication No. US 2009/0078225 to Hendriksma, hereinafter referred to as Hendriksma, the disclosure of which is incorporated herein by reference in its entirety. Hendriksma teaches a rocker arm with a rocker arm body within which is mounted a center high lift follower which is selectively allowed to pivot relative to the rocker arm body. A pair of low lift followers are mounted to the rocker arm body and flank the high lift follower. The high lift follower follows a high lift lobe of a camshaft to selectively transmit high valve lifting motion to a combustion valve while the low lift followers follow respective low lift lobes of the camshaft to selectively transmit low valve lifting motion to the combustion valve.
A locking mechanism is provided to selectively allow the high lift follower to pivot relative to the rocker arm body and to selectively prevent the high lift follower from pivoting relative to the rocker arm body. In order to position the locking mechanism to prevent the high lift follower from pivoting relative to the rocker arm body, thereby allowing high valve lifting motion to be transmitted to the combustion valve from the high lift lobe, pressurized oil is supplied to the locking mechanism through a circular oil passage originating in a rocker arm socket within which a tip of a lash adjuster is received. The pressurized oil urges a lock pin into engagement with the high lift follower.
Conversely, in order to position the locking mechanism to allow the high lift follower to pivot relative to the rocker arm body, thereby allowing low valve lifting motion to be transmitted to the combustion valve from the low lift lobes, oil is drained from the locking mechanism through the oil passage originating in the socket, and a lock spring pushes the lock pin out of engagement with the high lift follower. Consequently, the high lift lobe causes the high lift follower to pivot cyclically within the rocker arm body.
The rocker arm of Hendriksma is considered to be a default low lift two-step rocker arm because the rocker arm is placed in the low lift mode when no pressurized oil is supplied to the locking mechanism. It is known to provide a two-step rocker arm similar to the rocker arm of Hendriksma with the exception of modifying the locking mechanism to place the rocker arm in the high lift mode when pressurized oil is not supplied to the locking mechanism, thereby resulting in a default high lift two-step rocker arm. Such a modified locking mechanism is disclosed in FIG. 2 of U.S. Pat. No. 7,761,217 to Waters et al., hereinafter referred to as Waters, the disclosure of which is incorporated herein by reference in its entirety.
In order to allow the locking mechanisms of Hendriksma and Waters to respond sufficiently quickly to a desire to change operational positions, the oil passage must be sufficiently large to communicate oil therethrough in a sufficiently small amount of time. However, due to packaging constraints of the rocker arm, it may not be possible to increase the diameter of the oil passage without also increasing the size of other features of the rocker arm which also increases the overall packaging size of the rocker arm. Consequently, in the prior art, a compromise must be made between the packaging size of the rocker arm and the time required for responding to a change in operational positions of the locking mechanism. Furthermore, the response time of the lock pin can be sensitive to the circumferential orientation of the lash adjuster in the internal combustion engine due to misalignment of an oil inlet of the lash adjuster with the oil supply of the internal combustion engine.
What is needed is a rocker arm which minimizes or eliminates one or more of the shortcomings as set forth above.